Body tissue consists of cells and a tissue structure in a liquid environment in which metabolic products are transported between the cells and the blood vessels. For glucose monitoring especially in the case of diabetic patients it is possible to insert a probe into tissue for long periods in order to continuously collect constituents from the tissue fluid by means of diffusion processes and to determine the glucose content in the tissue from the effusate. This can be closely correlated with the blood glucose content without requiring an invasive access to the blood circulation. At the same time it is possible to administer an insulin-containing medication solution depending on the detected glucose concentration in order to thus create a sort of artificial pancreas. In the known systems with active substance dosing the construction is very complex and the system inserted into the body tissue is not realized in an integrated and miniaturized design. In particular there is a risk with rigid needle sensors that additional injuries to the surrounding tissue may occur while it remains in the body and as a result of which significant errors may occur in the determination of the analyte concentration.
On this basis the object of the invention is to avoid the disadvantages occurring in the prior art and to enable the determination of a constituent in the surrounding matrix and passage of a liquid in a simple manner using an implantable device and an appropriate method.